Method and apparatus for combusting finely divided low sintering temperature fuel



Feb. 26, 1952 D. DALIN ET AL 2,586,790

METHOD AND APPARATUS FOR COMBUSTING FINELY DIVIDED LOW SINTERINGTEMPERATURE FUEL Filed July s, 1946 S WM LQ/ E-JVZU 75212? TareL/bharvnes [T/bdblfk Patented Feb. 26, 1952 UNITED STATES PATENT OFFICEMETHOD AND APPARATUS FOR COMBUST- ING FINJELY DIVIDED LOW SINTERINGTEMPERATURE FUEL DavidDalin, Ronninge, and. Tore Johannes Hedbiick,Sodertalje, Sweden Application July 8, 1946, Serial No. 682,050 In-Sweden July 14, 1945 ranging in size from powder to coarsely crushed orwaste fuel granules such as screenings of the type ordinarily known asslack.

Heretofore the usual practice in combusting finely divided solid fuelshas been either to grind or crush the fuel to a fine powder and combustit in suspension or to use it in relatively coarser form and combust iton a grate of special construction. These two methods have sometimesbeen used in combination in the combustion of ash-rich fuels having ahigh sintering temperature, where the principal problem was disposal ofthe ash, and where the combustion temperature seldom or never exceededthe sintering temperature of the fuel. Heretofore, however, there hasbeen no feasible way of combusting ash-rich fuels having low sinteringtemperatures when such fuels were presented tothe combustion apparatusin the form of granules having a wide range of sizes. Such fuels mightbe crushed to a powder and burned wholly in suspension, as shown forexample by the patent to Cbutant, No. 1,703,814, issued February 26,1929, but this necessitated the expense of pulverizing the fuel, whichwas obviously objectionable. Nor was it possible to employ with suchfuels the device which had proven relatively successful with ash-richgranular fuels having higher sintering temperatures, namely the use of agrate constructed in such a way that the fuel bed was kept in constantmotion in an attempt to prevent ash and slag particles from stickingtogether to form large cakes which prevented combustion and weredifficult to discharge. Such moving grates were usually made as inclinedgrates, e. g., the Martin grate or Pluto stoker, and the grates werearranged as a sort of conveyor, fuel being introduced or fed to one endof the grate and ash being discharged at the other end, the combustionoccurring as the fuel was substantially horizontally carried across theinterval; However, even with such moving grates sintering could notalways be avoided, and even when they were successful their employmententailed certain serious disadvantages, the most obvious of whichresided in the fact that their first cost was high and it was virtually,impossible to prevent small ash particles from creeping into all of theslide faces of the grate parts and causing serious wear and damage,necessitating the furtlger expenses of frequent repair and replacemen 2It is, therefore, an object of the present invention to provide a.method for combusting, ash- -rich granular fuels having a relatively lowsintering temperature whereby such granular fuels, varying in size fromfine powder to coarse granules,

may be combusted at a high rate and with inexpensive apparatus.

A further and very important object of this invention resides in theprovision of a method and means for combusting fuel particles of awiderange of sizes without requiring sizing or crushing, which method andapparatus will permit particles. of such fuel, togbe simultaneouslycombusted in suspension and in a fuel bed, to thereby attain utmostcombustion efficiency de-- spite the wide difierences in particle sizes.

Another important. object of this invention resides in the provision ofa method and apparatus for combusting fuel of the character described inthe manner described in a furnace having a relatively small bottom area.

In furtherance of the foregoing object, it is another object of thisinvention to provide vertical travel of fuel particles in the fuel bedof apparatus of the character described instead of the horizontal fuelparticle travel which has heretofore characterized such apparatus.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel method ashereinafter described and more particularly defined by the appendedclaims, it being understood that such changes in the precise embodimentof the hereindisclosed invention may be made as come within the scope ofthe claims.

The accompanying drawing illustrates one complete example of thephysical embodiment of the invention constructed in accordance with thebest mode so far devised for the practical application of the principlesthereof, and in which:

Figure 1 is a vertical sectional view diagrammatically illustrating afurnace embodying this invention;

Figure 2 is a diagrammatic sectional view through the lower part of theinterior of the furnace chamber viewed from the left in Figure 1;

Figure 3 is a horizontal sectional view taken on the plane of the line3-3 in Figure 2;

Figure 4 is a top plan view of the furnace chamber shown in Figure 1;

Figure 5 is a vertical sectional view of the lower portion of a furnaceshowing a modified embod. iment of the invention; and i Figure 6 is afragmentary view illustrating a specific grate structure which may beemployed in the furnace of this invention.

Referring now more particularly to the accompanying drawing, the furnacechamber is indicated by I, the ashpit by 2, rotatable grate bars for theash by 3 and their bearing support by i.

Ducts for cooling medium are indicated by 5.

These ducts are arranged in such a way that they become embedded in thefuel charge as it settles onto the grate to form a fuel bed. The fairlyfinecrushed or more or less fine-grained fuel is introduced into thefurnace pneumatically through e. g. four nozzles 6 which are fed throughpipelines I, 8 from a mechanically driven fuel distributing device, e.g., screws 9, preferably one screw for each nozzle pipe-line, saidscrews issuing from a container II. The conveying air, which forms partof the required primary air (the other air is supplied from below thegrate) is admitted at l2 and entrains the fuel falling down through therespective branch pipe-line 8 and conveys it upwards through therespective pipelines I to the nozzles 6.

According to the invention the fuel is blown in and spread over thewhole furnace bottom. The smallest particles are combusted substantiallyin suspension, while the coarser particles fall down and are combustedon the furnace bottom to which combustion air (primary air) is admittedand from which the ash is conveyed away practically verticallydownwards. In order to prevent sintering in the fuel bed, combustionheat is abstracted from the bed by a fluid heat absorbing medium flowingin the ducts which traverse the bed as shown. These ducts are preferablyarranged as substantially vertically disposed finger-like pipe-coilsspaced from one another a distance to suit the fuel used and theprevailing combustion conditions. The arrangement of the pipe coils maybe seen in Figs. 1 to 3.

Channels for distributing primary air coming from below may be providedbelow the ducts or "fingers 5 and preferably these channels extendtransversely of the furnace. Thus, the natural falling down of the fuelis not prevented by unnecessary beams on which the fuel might getcaught. Alternatively, the channels l3 may be disposed above the pipecoils 5, as shown in Fig. 5. In order to prevent fuel from gettingcaught the channel systems should be adapted to be vibrated or shaken atuniform intervals. Any conventional means for vibrating or shaking thechannel system may be used, as for instance that shown in Figure 3. Inthis case a shaker bar 25 adapted to be reciprocated at uniformintervals by an eccentric 26 is located adjacent to one end portion ofthe channel system so that reciprocation of the shaker bar imparts avibrating motion to the channel system and thereby prevents fuel frombecoming lodged therein. As fuel is continuously added at the top of thefuel bed, ash is removed at the bottom thereof, dropping through therotatable grate bars 3 into the ashpit 2, to maintain the depth of thefuel bed substantially constant, and it will thus be seen that each fuelparticle is thus completely combusted in the course of vertical travelfrom top to bottom of the fuel bed.

The grate by means of which the ash is thus removed may have anysuitable form, although it is desirable that it should provide foragitating motion of the fuel bed in installations intended for thecombustion of fuel having a very high ash content. One suggested deviceis illustrated by Figures 1 and 2, employing a series of eccentrical- 1ymounted cylindrical grate bars, the axes of rotation of all of which aredisposed in a single plane. Adjacent pairs of grate bars are operatedsimultaneously, the two grate bars of each pair being moved in oppositedirections, as indicated by the arrows (see Figure 2), to provide ashearing movement of the fuel bed; and the individual pairs of gratebars are preferably arranged to have separately controllable rotationmechanisms to thereby regulate their discharge capacities in order tocompensate for irregularities in the fuel bed.

The discharge device shown in Figure 6 is suggested for use with morefinely divided fuels. In this device rotatable grate bars l8 and I9 aredisposed at spaced intervals, likewise arranged to be actuated in pairsbut mounted to rotate on their geometric axes. A segmental element 20 isoscillatably mounted beneath each pair of grate bars and is movedwhenever the grate bars move, so that a relatively large discharge maybe effected when desired, while preventing finely divided particles ofcombusting fuel from dropping down into the ashpit at times when thegrate is not operated. To further control discharge of ashes, a plate 2|is disposed between each pair of grate bars. In order to combustdescending fuel particles according to the invention it is desirablethat the particles fall down periodically on the furnace bottom so thatthe largest fuel pieces are ignited before further fuel covers the sameand prevents their ignition by radiation. This may be accomplished withimmovable nozzles by feeding fuel in equal quantity through two nozzles6 disposed opposite one another in the furnace walls. If most of thefuel is to be combusted in suspension, the nozzles are directed upwards.On the other hand, if a greater part of the fuel is to be combusted onthe grate, the nozzles are directed downwards. The fuel discharged fromthe nozzles is directed over the whole width of the furnace bed by meansof a guide device, for example. When a nozzle directed obliquelyupwardly is used the guide device may be dispensed with and the nozzlemay be formed as part of a conical surface, the fuel being spreadlaterally to the desired degree. The fact that part of the furnacebottom-a corner, for exampleis situated at a greater distance from thenozzle than the opposite wall, is compensated for by setting the angleof elevation of the nozzle directed toward the corner to that whichcorresponds to the greatest required length of throw, while the anglesof elevation for the nozzles discharging in the other directions aremade so that the lengths of throw are decreased proportionally and tothe desired degree. If the angle of elevation for the greatest distanceis chosen as 42, the angles for the other directions may be choseneither larger or smaller, all with the resultthat the length of throw isdecreased. The particles flung out from the nozzle fall down on thesurface of the furnace bottom in a narrow zone. The distance of theparticles from the nozzle is a function of the initial velocity ofdischarge from the nozzle, i. e. of the conveying-, gas, air-velocity or-quantity. However, if two or more nozzles are used, the velocity in thenozzles may be varied periodically. The

nozzles may receive their air from a common fan site nozzles are used,they are preferably arranged in such a way that each of them sweeps thebottom surface from the opposite wall to the middle. It is true that theconsequence of such an arrangement is that the paths of the particlescross one another, but this will not cause any serious difliculty, thedensity being not too great. Four nozzles, as shown in Fig. 4, may,however, be arranged in such a way that two nozzles located in oppositewalls-i. e. those placed diagonallywork at the same time, while thenozzles in the other diagonal are shut off, whereafter a reversal takesplace. The reversal is preferably effected by means of the guidemechanism for the distributing dampers, one of which, indicated by It,is visible at the bottom in Fig. 1.

To enable varying amounts of air to be fed to the pipe lines 1, aby-pass or shunt duct I 6, controlled by a damper ll, may be connectedin the primary air supply system to bypass excessive or undesiredamounts of such air into the ashpit (and thus into the fuel bed) insteadof permit ting all of it to flow out through the fuel lines and nozzles.

In order to dry the fuel in connection with the feeding of the samepreheated air should prefer ably be used as conveying medium. Bypreheating the air the ignition of the suspended fuel is alsofacilitated. From the foregoing description,

taken together with the accompanying drawing,

it will be readily apparent to those skilled in the art that thisinvention provides a method and apparatus for combusting relativelyfinely divided fuel of the type having a high ash content and lowsintering temperature when the same is in the form of granules of a widerange of sizes, from powder to coarse screenings, without requiring ahorizontally movable grate or the large furnace floor area concomitantthereto, and without requiring pulverization of the coarser granules.

Having now described our invention, what we claim as new and desire tosecure by Letters Patent is:

l. A furnace for combusting finely divided particles of high-ash fuel,which particles range in size from powder to relatively coarsescreenings, said furnace comprising: means defininga combustion chamber;nozzle means for injecting fuel particles of the character described,entrained in combustion air, into said chamber near the top thereof andin substantially even distribution throughout the horizontalcross-sectional area of the chamber; an ashpit below the combustionchamber and in communication therewith; grate means above the ashpit andbelow the combustion chamber; means for introducing combustion air intothe combustion chamber from below the grate means to enable the smallestfuel particles introduced into the combustion chamber to be combusted insuspension and to provide for complete combustion of the remainingparticles on a fuel bed of substantial height on said grate in thecourse of downwardmovement of such particles from the top of said fuelbed to the grate; and a plurality of vertical finger-like coils disposedat laterally closely spaced intervals in the portion of the bottom ofthe combustion chamber adapted to be occupied by the fuel bed andextending vertically substantially throughout the normal fuel bed heightof the combustion chamber and through which coolant fluid is adapted tobe circulated in indirect heat exchange relation with fuel in all partsof the bed in quantities and at a rate sufficient to maintain thetemperature of such fuel below its sintering point.

2. The method of combusting ash-rich low sintering temperature fuelparticlesv of a relatively wide range of sizes, from powder to coarsescreenings, wherein the combustion of the coarser pieces, due to thecharacter of the fuel, entails considerable time, which methodcomprises: introducing the fuel particles into a combustion chamber overburning fuel at a substantial distance above the bottom thereof with thefuel particles loosely dispersed and substantially evenly distributedover the horizontal area of the chamber so that the individual particlesare accessible from all directions whereby the finer particles areburned in suspension and the coarser pieces drop to collect at thebottom of the combustion chamber; confining the coarser pieces whichcollect at the bottom of the combustion chamber to a bed of substantialdepth so that a large volume of fuel may be combusted in a combustionchamber of relatively small horizontal area despite the long timerequired for combustion of the fuel which forms the bed; removing theash resulting from combustion of the fuel in the bed; and continuouslycirculating cooling fluid through the fuel bed in heat exchange relationtherewith, but not in contact therewith, with the cooling fiuid movingalong paths distributed throughout the entire bed. and reachingsubstantially the full depth thereof so that the cooling influence ofthe cooling fluid reaches all portions of the bed to maintain thetemperature of the fuel bed below that at which it sinters.

3. The method of combusting ash-rich low sinterin temperature fuelparticles of a relatively Wide range of sizes, from powder to coarsescreenings, wherein the combustion of the coarser pieces, due to thecharacter of the fuel, entails considerable time, which methodcomprises: introducing the fuel particles into a combustion chamber overburning fuel at a substantial distance above the bottom thereof with thefuel particles loosely dispersed and substantially evenly distributedover the horizontal area of the chamber so that the individual particlesare accessible from all directions whereby the finer particles areburned in suspension and the coarser pieces drop to collect at thebottom of the combustion chamber; constraining the burning fuel bed todownward movement in a column of relatively small horizontal area sothat to afford sufficient time for combustion of the coarser pieces andenable the combustion of a large volume of fuel per unit of time, a bedof substantial depth must be maintained; removing the ash resulting formcombustion of the fuel in the bed from the bottom thereof; andcontinuously circulating cooling fluid through the fuel bed in heatexchange relation therewith, but not in contact therewith, with thecooling fluid moving along paths distributed throughout the entire bedand reaching substantially the full depth thereof so that the coolinginfluence of the cooling fluid reaches all portions of the bed tomaintain the temperature of the fuel bed below that at which it sinters.

4. A furnace for combusting ash-rich low sintering temperature fuelparticles of a relatively wide range of sizes, from powder to coarsescreenings, comprising: means defining an upright combustion chamber ofrelatively small horizontal area; means defining an ash pit below thecombustion chamber and communicated therewith; a grate defining thebottom of the combustion chamber; means for introducing combustion airinto the combustion chamber; means located'a substantial distance abovethe grate for introducing the fuel particles into the combustionchamber; means for effecting loose dispersion and substantially evendistribution of the fuel particles over the horizontal area of thecombustion chamber so that the individual particles are accessible fromall directions whereby the finer particles may be combusted insuspension and the coarser particles collect in a bed on the grate; andducts for fluid heat exchange medium substantially uniformly distributedthroughout the space in the bottom of the combustion chamber andextending a substantial distance above the grate so that the coolinginfluence of the medium circulated through the ducts reaches asubstantial distance above the grate, whereby a fuel bed of substantialdepth may be maintained without sintering.

5. In a furnace for combusting ash-rich low sintering temperature finelydivided solid fuel of the type in which fuel particles of various sizesare injected into a combustion chamber at a point spaced above thebottom of the chamber to be partially combusted in suspension, theremainder of the combustion occurring in a fuel bed at the bottom of thecombustion chamber; a grate means at the bottom of the combustionchamber and upon which fuel injected into the combustion chamber and notcombusted in suspension is adapted to'lie to be combusted in a fuel bed,the sides of the combustion chamber constraining the fuel bed todownward movement as combustion thereof proceeds; means including fuelinjection nozzles for injecting solid fuel particles of a wide range ofsizes into the combustion chamber at a substantial distance above thegrate means with said particles loosely dispersed and substantiallyuniformly distributed 8 i so that the individual particles areaccessible from all directions whereby the finer particles may becombusted in suspension and the coarser particles drop to form a fuelbed of substantially uniform thickness on said grate means; and aplurality of substantially vertical heat exchange coils uniformlydistributed across the bottom of the combustion chamber and of a heightto extend upwardly a substantial distance from the top of said gratemeans, so that the cooling REFERENCES CITED The following-references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 572,077 Smith Nov. 24, 18961,703,814 Coutant Feb. 26, 1929 1,734,669 Frisah Nov. 5, 1929 2,183,496Peters Dec. 12, 1939 FOREIGN PATENTS Number Country Date 325,964 GreatBritain Mar. 6, 1930 334,757 Great Britain Sept. 11, 1930

1. FURNACE FOR COMBUSTING FINELY DIVIDED PARTICLES OF HIGH-ASH FUEL,WHICH PARTICLES RANGE IN SIZE FROM POWDER TO RELATIVELY COARSESCREENINGS, SAID FURNACE COMPRISING: MEANS DEFINING A COMBUSTIONCHAMBER; NOZZLE MEANS FOR INJECTING FUEL PARTICLES OF THE CHARACTERDESCRIBED, ENTRAINED IN COMBUSTION AIR , INTO SAID CHAMBER NEAR THE TOPTHEREOF AND IN SUBSTANTIALLY EVEN DISTRIBUTION THROUGHOUT THE HORIZONTALCROSS-SECTIONAL AREA OF THE CHAMBER; AN ASHPIT BELOW THE COMBUSTIONCHAMBER AND IN COMMUNICATION THEREWITH; GRATE MEANS ABOVE THE ASHPIT ANDBELOW THE COMBUSTION CHAMBER; MEANS FOR INTRODUCING COMBUSTION AIR INTOTHE COMBUSTION CHAMBER FROM BELOW THE GRATE MEANS TO ENABLE THE SMALLESTFUEL PARTICLES INTRODUCED INTO THE COMBUSTION CHAMBER TO BE COMBUSTED INSUSPENSION AND TO PROVIDE FOR COMPLETE COMBUSTION OF THE REMAININGPARTICLES ON A FUEL BED OF SUBSTANTIAL HEIGHT ON SAID GRATE IN THECOURSE OF DOWNWARD MOVEMENT OF SUCH PARTICLES FROM THE TOP OF SAID FUELBED TO THE GRATE; AND A PLURALITY OF VERTICAL FINGER-LIKE COILS DISPOSEDAT LATERALLY CLOSELY SPACED INTERVALS IN THE PORTION OF THE BOTTOM OFTHE COMBUSTION CHAMBER ADAPTED TO BE OCCUPIED BY THE FUEL BED ANDEXTENDING VERTICALLY SUBSTANTIALLY THROUGHOUT THE NORMAL FUEL BED HEIGHTOF THE COMBUSTION CHAMBER AND THROUGH WHICH COOLANT FLUID IS ADAPTED TOBE CIRCULATED IN INDIRECT HEAT EXCHANGE RELATION WITH FUEL IN ALL PARTSOF THE BED IN QUANTITIES AND AT A RATE SUFFICIENT TO MAINTAIN THETEMPERATURE OF SUCH FUEL BELOW ITS SINTERING POINT.